A current in a power converter or other electronic devices is often an important operating characteristic that often should be replicated or sensed with a signal, generally with minimal delay (i.e., with wide bandwidth). A signal that replicates a current provides an indicator that the power converter or other electronic device is operating at or near maximum performance. The signal can also be employed to prevent component damage when an over-current event or a short circuit is encountered.
Conventional arrangements to provide a signal that replicates a current generally operate in a single quadrant (i.e., a current is sensed in only one direction and with a positive voltage). Sensing a current in power converters such as dc-dc power converters is usually performed in a two-quadrant mode (i.e., a signal is produced that senses a bidirectional current and with a positive voltage). If two-quadrant sensing is necessary, a conventional arrangement duplicates the circuit that provides the current-replicating signal, thereby increasing the cost, component count and circuit area.
Producing a signal that replicates a current is often done using a current sense resistor external to a high-gain operational amplifier. Separation of the current sense resistor from the operational amplifier leads to inaccuracy and temperature-dependent results due to mismatching of component characteristics. Some integrated current-sensing solutions employ a scaled version of power switches coupled in parallel with the power switches to sense current therein. This approach can be accurate, but involves complex and often duplicated circuitry, and is still sensitive to component mismatching and manufacturing process variations.
There is often a need to sense a current in a power converter that is divided between two circuit components such as two alternately-conducting power switches employed in a buck power converter topology. The current sensing should be performed at each of the two circuit components rather than in the circuit before or after division of the circuit between the two circuit components. There is a further challenge to sense divided currents when there is a substantial dc bias between the two circuit components.
Thus, there is an unanswered need to provide a circuit structure and method to provide a signal that accurately replicates a current that is conducted by two circuit components in a power converter or other electronic device, which can be a bidirectional current. The resulting circuit structure should be substantially insensitive to an operating temperature and manufacturing variations. Accordingly, what is needed in the art is a circuit structure and method of forming and operating the same that overcomes the deficiencies of current designs.